1964-1990 Crank Types Identification



There are six types of cranks:

  1. Early series big block, short stroke, all forged. 400, 425's have 'em. They have an "L" or "check mark" shaped notch on the drive flange.

  2. Early series small block. Forged. All 330's. Notch on back drive flange is "L" or "check mark" shaped like other forged cranks.

  3. Late series small block. Maybe nodular, most cast, non forged. 260, 307, 350, 403. Notch on back drive flange is a tall "C" or flat "U" shape. Later [sb] cranks, which are even lamer, use an even deeper C-notch, almost as deep as it is wide. Some have the "L" or "check mark" shaped notch, but they are not forged. Check the casting parting line: wide means forged, narrow means cast.

  4. Late [1968 and up] big blocks: 400, 455. Forged. Mystery crank - reputed to have been used in '68 Toronado, but found in a 1968 low comp. 2bbl fullsize motor. ID number 400943. Notch on back drive flange is "L" or "check mark" shaped like other forged cranks. Check the casting parting line: wide means forged, narrow means cast.

  5. Late bb's, cast, Nodular iron. Casting #397363 +/- the last digit. Has a big ol' N cast onto the side of the front weight. Best 455 crank you can get, unless you count the elusive 'forged' unit mentioned above. Apparently, they came in a lot of 1968 to 1969 400's, and 1968 to 1970 455's. Maybe later engines, too. External ID: back drive flange notch is a tall "C" or wide "U" shape, like every other cast crank, big or little block. 'Course, from the outside, it looks just like...

  6. Late bb's, cast, plain iron. Same casting #397363, +/-. It has NO 'N' on the front weight, yet has the same casting #, go figure. Same tall "C" or wide "U" shaped notch cast into the back drive flange. Weaker than the Nodular crank, or so they say.

The bad new is there's no way to tell a Nodular crank from a plain Jane with the oil pan on. You have to wait and look for the big 'ole N. The good news is- A forged crank is easily id'd by the L-shaped notch in the OD of the drive flange.

With the pan off or the crank out, there are two ways to tell a forged crank.

  1. Parting line. Wide = forged. Thin = cast. If there, guarantees a forged crank.
  2. Notch in rear flywheel mounting flange. L-shaped = forged. U-shaped = cast. Caution: some 1968-69 cast small block cranks had this notch. Check parting line for sure.
[ Thanks to Chris Witt, Bob Barry for this information ]
Number   CID   Year(s)     Notes
230376   SB
390275   403   '77 - '79   Balance hole in the 1st throw, groove on the #1 counterweight.
393654   350   '74         Plain iron. No 'N' on front weight. Balance hole in 1st throw.
                           "C" notch ¼" deep, 1" wide.
397363   455   '68 - '70   Nodular iron. 'N' on front weight.
397363   455   '72 - '76   Plain iron. No 'N' on front weight.
398261   SB
400943   455   '68         Forged Steel. In fullsize, w/2bbl, w/tow package.
418882   SB
556607   350   '77         Plain iron. No 'N' on front weight. No balance hole.
                           "C" notch 5/8" deep, 1" wide.
556607   307   '85         This might be the wrong. '77 350 is positive.

One handy way to divide Olds V-8's is EARLY [pre 1968] vs. LATE [1968 and up]. One of the most notable differences in the two groups is in crankshafts. Early engines all had forged steel crankshafts, whereas late engines [almost] all had cast iron crankshafts. Furthermore, the bolt pattern on the rear face, where the flywheel or flexplate attaches, is different. The early pattern has one hole offset CCW about 5 degrees from a perfect hex pattern, whereas the late pattern has that hole, and a second hole as well, offset in the other direction about the same amount. Thus, the two are not interchangeable. Early cranks [330, E-400, 425] require an early pattern flexplate, and all other engines use the late pattern.

Quick, low-hassle ID tip: On the back of the crank, on the OD of the flange to which the flexplate or flywheel attaches, is a notch. Forged cranks [330, early 400, 425] have an L-shaped notch. Cast cranks [350, almost all 455's, late 400 engines] have a notch shaped like a tall C (or a wide U).

Early big block forged steel crankshafts carried ID #390370 or 384722. This unit, used in the 442's early 400 engines and all 425's, has a stroke of 3.975". This crank can make an early 400 engine [using a 4.000" bore E block], or a 425 [with a 4.125" bore A, D, or F block and 425 pistons and rods], or a 455 small block [with a 350 Diesel block and about $3000 worth of Mondello parts]. A 455 big block cannot be made from this crank.

For 455 use, you will almost certainly be using a cast crankshaft. These cast 455 cranks come in two kinds, unfortunately with the same casting number (397363). The better unit is made of "nodular iron" and indicates this proudly with a big N, about an inch tall, cast onto the side of the front counterweight.

Judging from where they have been found, these cranks apparently came in most 455's from inception in 1968 up until about 1972. Of course, 442/Toro/W-30 motors were more likely to have the best parts, including the Nodular crank... of these, you are more likely to find a Toronado as a cheap engine donor. [Also found in '70 Delta 88]

[ Thanks to Chris Witt for this information ]